/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.tomcat.util.security;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.HashMap;
import java.util.Map;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

/**
 * A thread safe wrapper around {@link MessageDigest} that does not make use
 * of ThreadLocal and - broadly - only creates enough MessageDigest objects
 * to satisfy the concurrency requirements.
 */
public class ConcurrentMessageDigest {

	private static final String MD5 = "MD5";
	private static final String SHA1 = "SHA-1";

	private static final Map<String, Queue<MessageDigest>> queues =
			new HashMap<String, Queue<MessageDigest>>();

	static {
		try {
			// Init commonly used algorithms
			init(MD5);
			init(SHA1);
		} catch (NoSuchAlgorithmException e) {
			throw new IllegalArgumentException(e);
		}
	}

	private ConcurrentMessageDigest() {
		// Hide default constructor for this utility class
	}

	public static byte[] digestMD5(byte[]... input) {
		return digest(MD5, input);
	}

	public static byte[] digestSHA1(byte[]... input) {
		return digest(SHA1, input);
	}

	public static byte[] digest(String algorithm, byte[]... input) {

		Queue<MessageDigest> queue = queues.get(algorithm);
		if (queue == null) {
			throw new IllegalStateException("Must call init() first");
		}

		MessageDigest md = queue.poll();
		if (md == null) {
			try {
				md = MessageDigest.getInstance(algorithm);
			} catch (NoSuchAlgorithmException e) {
				// Ignore. Impossible if init() has been successfully called
				// first.
				throw new IllegalStateException("Must call init() first");
			}
		}

		for (byte[] bytes : input) {
			md.update(bytes);
		}
		byte[] result = md.digest();

		queue.add(md);

		return result;
	}

	/**
	 * Ensures that {@link #digest(String, byte[][])} will support the specified
	 * algorithm. This method <b>must</b> be called and return successfully
	 * before using {@link #digest(String, byte[][])}.
	 *
	 * @param algorithm The message digest algorithm to be supported
	 * @throws NoSuchAlgorithmException If the algorithm is not supported by the
	 *                                  JVM
	 */
	public static void init(String algorithm) throws NoSuchAlgorithmException {
		synchronized (queues) {
			if (!queues.containsKey(algorithm)) {
				MessageDigest md = MessageDigest.getInstance(algorithm);
				Queue<MessageDigest> queue =
						new ConcurrentLinkedQueue<MessageDigest>();
				queue.add(md);
				queues.put(algorithm, queue);
			}
		}
	}
}
